My site has about 300IP/4000pv per day, 40% new visitors, 20% from search engine and 70% direct input. But most of the visitors come from the same district of US. My adsense was banned on Monday of this week. I swear that I didn't click any ads and never told a friend about my site. I think it is because of visitors too centralized. Now I am using bidvertiser, adbrite and buy.at networks. Do you think is there any risk in this traffic condition? If yes, what should I do to control this risk?